For people aged 15-45 years old suicide is the most common cause of death in industrial countries in the world. One million people commit suicide every year in the world. In Sweden four persons take their lives every day and another 40-60 persons try to take their lives every day.
In Sweden as in other countries, it has traditionally been very difficult to identify those depressed patients who really constitute a risk group for suicide. The only method that has been available so far in traditional health care to identify whether there is a suicide risk has been based on personal interviews by a psychiatrist or other available health care professional and the patients own response to certain standard forms. Such methods are characterized by being fairly subjective. The outcome of such investigations depends on the experience of the health care professional and the way of valuing the interview answers from the patients and therefore tend to be rather arbitrary. The reliability also suffers from the fact that suicidal patients sometimes deliberately withhold suicide plans for the health care professional in order to remove any obstacles to the planned suicide. For example, it has been found that almost 80% of inpatients who take their lives denies such plans in the last week before their suicide.
It has previously been demonstrated by the research of associate professor Lars-Håkan Thorell that there is a strong relationship between the so-called hyporeactivity and suicidal tendencies, while it also has been shown that there is a corresponding strong relation between normal reactivity and “non-suicidal tendencies”. It has been shown that the degree of hyporeactivity can be measured objectively and quantitatively by a particular test procedure developed by Lars-Håkan Thorell.
Based on the research developed by associate professor Lars-Håkan Thorell for 25 years, the company Emotra AB, since its start 2001, has developed such a clinically useful and entirely objective method that can be used as a support in the clinical evaluation of suicide risk among depressed patients. The method is based on the use of the so-called EDR tests (Electro Dermal Reactivity), in which tests the ability of the skin (derma) to lead a weak current is utilized, and which has led to the so-called EDOR test (Electro Dermal Orientation Reactivity). The measurements performed according to the EDOR test include among other things electro dermal effects based on the ability of the skin to lead a weak current via the fingertips. The more a person is responding with attention in his brain on a signal, the more sweat glands are activated. The channels of the sweat glands are filled to the skin surface, thus forming more current paths through the skin which in itself has a high electrical resistance so that a larger current is measured.
By testing the response of the patients to certain experimentally well defined sound signals or tones, it has been possible to identify those patients who are so-called electrodermal hyporeactive, i.e. persons who do not show interest in the tones. By definition, hyporeactive persons react very little on signals which is rare among healthy individuals or depressed persons who are not suicidal. However, to react very little to the signals is very common for suicidal depressed patients. A test of this kind will take approximately 15 minutes to complete.
Hyporeactivity implies a strong indication of long-term suicidal propensity among depressed individuals. Once it has been established that a person is hyporeactive, it can be assumed that this state lasts at least 1-2 years. In combination with a severe depression an observed hyporeactivity involves a significant risk for suicide. The method does not claim to replace traditional psychiatric examinations, but is best suited as a supporting complement to the traditional methods. The objectively measured values then gives valuable information about the extent to which the tested person needs treatment, mainly to prevent suicide, but also to treat the depression itself.
The EDOR test measures two different phenomena that differ for people with a hyporeactive dysfunction.                Orientation function—discovered by Pavlov in 1927 and described as “the attention paid to a new event”,        Habituation of the orientation reaction—was described by Sokolov in 1963 and involves a learning not to unnecessarily react to such events that constitute the normal environment.        
Upon exposure of a specific event, persons with a hyporeactive dysfunction show a rather clear pattern of reaction in the form of an often normal orientation reaction to new events, but an extremely fast habituation, i.e. the person finish to care about the event (incident) too soon.
The EDOR test measures the orientation reaction from a well-defined event, a tone. The strength of the reaction is measured as the degree of the changes in the skin conductance and blood flow in the finger tips. Skin conductance is defined as the ability of the skin to lead a small electric current. The skin conductance is measured by providing a current between two electrodes on the finger tips, and the stronger reaction of the patient, the more sweat glands have been activated and the more current is passed through the skin. Furthermore, at a reaction the blood flow through the blood vessels is altered as the vessels constrict. Also the pulse becomes slower and the respiration decreases. By repeating the event, i.e. the tone, the habituation of the orientation reaction can be measured.
In FIG. 3 (below) it is illustrated two typical examples of response to tone stimuli from a reactive and a hyporeactive person, respectively.
The EDOR test itself is not further described here, but it is referred to the studies published by Thorell 2009-2013 as well as to the accompanying literature list.
In WO 02/01478 it is described more generally electrodermal measurements and psychophysiology. This publication describes a small mobile wireless communication system that enables interaction between two or more people so that each one can experience psychophysiological signals, such as visual-, auditory- and/or sensory signals, from one or more of the other interacting persons. This can be possible by means of small, simple and inexpensive electronic solutions and signal codes, as described in the patent publication, and a signal transmitting network, such as Internet or a mobile/telephone network. It is implied in the publication that the system might be used in a “Depression—or suicide research/clinic”, but it is not further described how this could be done.
At the EDOR test a special apparatus is used to measure the biological signals from the brain to detect depressed patients who are at risk for suicide. The apparatus comprises a handheld measuring unit with sensor means for measuring electrodermal activity in the fingers of the patients. In addition to the handheld measuring unit the apparatus also comprises headphones and a computer for the analysis of the measurements. The measuring unit transmits an experimentally well defined, specific tone to the patient through the headphones. The tone is repeated according to a specific, tested schedule in widely varying intervals around about 40 seconds. The electrodermal activity of the patient is measured throughout the entire test which takes 15 minutes.
The measuring unit has a size similar to a conventional spectacle case. The measuring unit is placed on the desk in front of the patient/test person. Sensor means in the form of skin conductance electrodes for measuring the electrodermal activity are mounted on the upper side of the measuring unit and on which the patients are allowed to place their fingers during the test.
If the psychiatric health care should be able to rely on a test of this kind, that aims to serve as a routine method for the assessment of suicidal propensity, the test must be very reliable, i.e. the test must have a significant high precision. In order for the test to be sufficiently reliable it must be carried out under almost ideal conditions, so that no external factors are affecting the test and it must be performed in such a way that all the factors/variables that might affect the test result are controlled.
So far it has been difficult to reach ideal conditions and it has not been possible to check all affecting variables. For that reason it has heretofore also been necessary to accept some uncertainties in the interpretation of the measuring result. Such uncertainties might be unacceptable for the mental health care to rely on the test, or alternatively, it requires an extensive and time consuming extra analysis to interpret the results and identify a hyporeactive patient.
Although misinterpretations are rare in the tests it might happen, The reasons for misinterpretations could be that the current test only relies on sound stimuli for the measurement of electrodermal activity. The testing process is thus affected by undesirable interference from the surrounding environment, such as noise interference, which might reduce the precision of the measuring result. Moreover, tremors and other nervous reactions of the patient might adversely affect the testing process. Furthermore, in the existing test procedure there is no possibility to control a number of variables that each one has a particular influence on the interpretation of the measuring result. The weaknesses identified in the existing test increases the demands of skill of the health care professional who interprets the measuring result and the reliability of the interpretation of the measuring result is then somewhat reduced and thus the precision of the test.
It has also been found a small percentage of depressed patients who do not show any reaction at all at the electrodermal measurement and at the same time a very low electrical conductance. In these cases it is supposed that the sudomotorical (sweat) system for some reason has been destroyed, but it might be another reason, that the patient is not at all responsive to the orientation reactions. If the electrodermal system is destroyed but the orientation reactions are existing in the brain, then these reactions can be detected as peripheral blood volume changes (e.g. blood volume decrease in the fingers) and central (blood volume increase in the brain) and a slower pulse rate of the patient. In case no orientation reactions can be detected in the blood volume and pulse rate of the patient this strengthen the suicidal propensity.
It is an object of the present invention to reduce/eliminate source of errors of the kind mentioned above and thus ensuring a higher precision in the analysis of the measuring result and/or facilitate the analysis required for the interpretation of the test result.